1. Field of the Invention
The present invention generally relates to a bearer integration method and an apparatus for the method. More particularly, the present invention relates to a bearer integration method and apparatus for integrating a plurality of bearer services to a wireless channel by time-division multiplexing/demultiplexing with baseband processing.
In a wireless communication in a CDMA system, since a plurality of terminal (mobile) stations use the same radio frequency, the CDMA system is controlled such that each terminal communicates with smaller power by using several technologies such as soft handoff. In addition, interference is suppressed so as to increase the number of available wireless channels. Further, in the CDMA system, a plurality of bearer services can be used via a terminal station. In this case, if a wireless channel is used for each of the bearer services, wireless channels and the power can not be used effectively. Therefore, a plurality of bearer services are integrated to a wireless channel by time-division multiplexing/demultiplexing with baseband processing. Thus, it is required to perform such bearer integration effectively with no instantaneous interruption.
2. Description of the Related Art
FIGS. 1–5 are figures for explaining a conventional technique. FIG. 1 shows a part of a mobile communication system of CDMA according to the conventional technique. In the figure, the numeral 1 indicates a mobile station or a terminal station, the numerals 8, 9 indicate terminal apparatuses (TE-A, TE-B) which are connected to the mobile station 1 wherein each terminal apparatus terminates a bearer service, the numeral 2 indicates a base station (BTS) for performing wireless communication with the mobile station 1 by CDMA, the numeral 3 indicates a base station control apparatus which performs bearer integration control and the like, the numeral 4 indicates a mobile exchange (MSC), the numeral 100 indicates a public network (PSTN), and the numerals 6, 7 indicate terminal apparatuses (TE-C, TE-D) which is connected to the public network 100 and terminate a bearer service.
The terminal apparatus 8 (TE-A) communicates with the terminal apparatus 6 (TE-C) by a bearer service. The mobile station 1 and the base station 2 use a wireless channel (for example m1). In this state, when a new bearer service is required between the terminal apparatus 9 (TE-B) and the terminal apparatus 7 (TE-D), if a wireless channel (for example m2) which can accommodate bearer services for two channels is available, the base station control apparatus 3 releases the wireless channel m1 which is already used and instructs the mobile station 1 and the base station 2 to use the wireless channel m2. Thus, the base station control apparatus 3 time-division multiplexes (bearer integrates) each bearer service for downward transmission and the mobile station 1 time-multiplexes each bearer service for upward transmission. Then, communication is carried out by using the wireless channel m2. When the base station control apparatus 3 cannot keep the wireless channel m2, it keeps a wireless channel (for example m3) which is available at the time and instructs the mobile station 1 and the base station 2 to use the wireless channels m1 and m3 for providing the bearer service between the terminal apparatus 9 (TE-B) and the terminal apparatus 7 (TE-D). After that, when the wireless channel m2 becomes available, the wireless channels m1 and m3 are released and the base station control apparatus 3 instructs the mobile station 1 and the base station 2 to use the wireless channel 2 m2.
FIG. 2 shows a basic configuration of a send/receive processing part (which does not support bearer integration) in the mobile station 1. This configuration is the same as the send/receive processing configuration for a circuit between the mobile station 1, the base station 2 and the base station control apparatus 3.
As shown in FIG. 2, the send/receive processing configuration includes a send processing part 10 and a receive processing part 30. The send processing part 10 includes a bearer interface part 11, a frame processing part 12 for adding a frame header identifier and the like for a wireless frame, an error correction encoding part 13 using convolutional code and the like, a symbol repeating part 14 for converting a symbol speed to a speed suitable for the chip rate even when using different data transmission rate, an interleaving part 15 for distributing each symbol in a frame unit, a spreading modulator 16 for spreading the symbol by a spreading code, a baseband filter 17, a D/A converter 18, a send IF part 19, a send wireless part 20, a send filter+antenna part 21, and a send control part 22 for controlling above-mentioned each part.
The receive processing part 30 includes a receive filter+antenna part 31, a receive wireless part 32, a receive IF part 33, an A/D converter 34, a baseband filter 35, a RAKE receive part 36 for synthesizing despreading code by a plurality of fingers, a deinterleaving part 37, a symbol extracting part 38 for extracting data from an input symbol by data extracting clock corresponding to a specified transmission rate, an error correction decoding part 39 using Viterbi decoding and the like, a bearer interface part 41 and a receive control part 42 for controlling above-mentioned each part.
The RAKE receive part 36 includes a finger part 361, a delayed lock loop (DLL) part 362, a searcher part 363, and a synthesizing part 364.
In the relation between the base station 2 and the base station control apparatus 3, the bearer interface part 11 of the downward line, the frame processing part 12, the frame processing part 40 and the bearer interface part 41 of the upward line are included in the side of the base station control apparatus 3. Other configuration is included in the side of the base station 2.
In the send processing part 10, data transmission rate can be changed by changing spreading codes set in the spreading modulator 16 and data transmission rate set in the symbol repeating part 14. In the receive processing part 30, a receive wireless channel and the data transmission rate can be changed by changing spreading codes set in the finger part 361 of the RAKE receive part 36 and data transmission rate set in the symbol extracting part 38.
FIG. 3 is a timing chart showing communication switching to a wireless channel of a different data transmission rate. Generally, a wireless channel is distinguished by using a different spreading code, and data of different transmission rates are spread by the same chip rate in CDMA. In addition, all wireless channels sent from a base station and each terminal station are synchronized with a system clock and frame timing of the system. The terminal station 1 can extract the chip rate by receiving a pilot channel sent from the base station 2 so as to generate the system clock. In addition, the terminal station 1 extracts frame timing by receiving a sync channel sent from the base station 2. Therefore, switching between wireless channels is realized only by switching the spreading code according to the frame timing. Thus, it is not necessary to re-synchronize the clock or the frame. Further, even when each data transmission rate of wireless channels to be switched is different, since a receive signal which can be received in the same chip rate can be realized by switching a setting which defines the number of chips for one bit according to the frame timing. Thus, switching without an instantaneous interruption can be achieved.
An example of wireless channel (transmission rate) switching will be described with reference to FIG. 3. As for the wireless channel A, assuming that the data rate=Ad and the spreading code=Ap. As for the wireless channel B, assuming that the data rate=Bd (=2×Ad) and the spreading code=Bp. In the send processing part 10, the send control part 22 sets the data transmission rate=Ad in the symbol repeating part 14 and sets the spreading code=Ap in the spreading modulator 16 for sending the wireless channel A. When wireless channel switching is requested in this state, the send control part 22 sets the transmission rate=Bd in the symbol repeating part 14 and sets the spreading code=Bp in the spreading modulator 16 in synchronization with a send switch timing t which is determined between the send processing part 10 and the receive processing part 30 beforehand. The wireless channel B is sent from this time.
In the receive processing part 30, the receive control part 42 sets the spreading code=Ap in the finger part 361 in the RAKE receive part 36 and sets the data transmission rate=Ad in the symbol extracting part 38 for receiving the wireless channel A before the switch timing t. When wireless channel switching is requested, the receive control part 42 sets the transmission rate=Bd in the symbol extracting part 38 and sets the spreading code=Bp in the finger part 361 in synchronization with a receive switch timing t which is determined between the send processing part 10 and the receive processing part 30 beforehand. The wireless channel B is received from this time. Since the receive processing part 30 performs receive processing according to the system clock/frame timing which are extracted, switching between wireless channels of different data rates can be realized without instantaneous interruption by synchronizing the receive switching timing t with the frame timing.
FIG. 4 shows a basic configuration of send/receive processing parts (which support bearer integration) of the mobile station 1 according to a conventional technique. This configuration shown in FIG. 4 is equivalent to a send/receive processing configuration for one circuit realized between the mobile station 1, the base station 2 and the base station control apparatus 3. The send processing part 10 includes two systems (“a” system and “b” system) from a bearer interface part 11 to a baseband filter 17, a bearer multiplexing part 23 for multiplexing two bearer services in synchronization with the frame timing at the time of bearer integration and a wireless channel multiplexing part 24 for multiplexing two wireless channels into a wireless signal of the same frequency before bearer integration. The receive processing part 30 includes two systems (“a” system and “b” system) from a baseband filter part 35 to a bearer interface part 41, a wireless channel demultiplexing part 43 for demultiplexing the two wireless channels which were multiplexed before bearer integration and a bearer demultiplexing part 44 for demultiplexing the two bearer services which were multiplexed at the time of bearer integration in synchronization with the frame timing.
In FIG. 4, processing routes for bearer services before bearer integration are shown with solid line arrows. In the send processing part 10, input bearer services (1) and (2) are spread into wireless channels m1 and m2 of the same frame timing by spreading codes of spreading modulation parts 16a and 16b respectively. After that, the wireless channel multiplexing part 24 multiplexes the wireless channels into wireless signals of the same frequency. Then, the wireless signals are sent. In the receive processing part 30 which receives the wireless signals, the wireless channel demultiplexing part 43 demultiplexes the multiplexed wireless signals into the wireless channels m1 and m2 and inputs the channels to the wireless channel processing parts 30a and 30b respectively. Then, the wireless channels m1 and m2 are demodulated by spreading codes of the RAKE receive parts 36a and 36b respectively. Then, the bearer services (1) and (2) are output.
Processing routes for bearer services when bearer integration is performed are shown with dotted line arrows in FIG. 4. When bearer integration is requested in the above-mentioned state, the bearer multiplexing part 23 starts time-division multiplexing for the bearer services 91), (2) with frame timing which is predetermined between the bearer multiplexing part 23 and the receive processing part 30. At the same time, a wireless channel m3 is set in the symbol repeating part 14b and the spreading modulation part 16b. After that, multiplexed data which is multiplexed by the bearer multiplexing part 23 is sent by the wireless channel m3 which has the same frame timing. In the receive processing part 30 which receives the wireless channel m3, the RAKE receive part 36b and the symbol extracting part 38b are set for the wireless channel m3 in synchronization with the frame timing which is predetermined between the receive processing part 20 and the send processing part 10. At the same time, the bearer demultiplexing part 44 starts to demultiplex the bearer service. Accordingly, the bearer services (1) and (2) provided by the wireless channels m1 and m2 are integrated into the bearer services (1) and (2) provided by the wireless channel m3 without instantaneous interruption.
As mentioned above, according to the conventional bearer integration method, bearer integration can be performed without instantaneous interruption as long as the bearer integration is performed between the wireless channels m1, m2, m3 which have the same frame timing.
Generally, in order to increase the number of wireless channels in CDMA wireless communication, each terminal station performs communication with smaller amount of power. In addition, the system provides frame offsets which are different for each wireless channel such that the wireless power is not concentrated in a time period. Therefore, in such a communication system, there is a very low possibility that a wireless channel of the same frame offset is unoccupied when performing bearer integration. In most cases, a wireless channel of a different frame offset should be assigned.
FIG. 5 shows a timing chart for performing bearer integration between wireless channels of different frame offsets according to the conventional technique. For example, a period T of a reference frame is 20 ms in which the reference frame is divided into 16 frame offsets.
Before bearer integration, in the bearer service A, data communication is performed in synchronization with a timing which is shifted by the frame offset A from the reference frame timing. In the bearer service B, data communication is performed in synchronization with a timing which is shifted by the frame offset B from the reference frame timing.
When integration of the bearer services A and B is requested, the base station control apparatus 3 acquires, for example, the wireless channel C which is unoccupied, and starts bearer integration control in synchronization with bearer integration timing t (which is shifted by the frame offset C from the reference frame timing). At this time, since the timing for capturing the bearer services A and B in the wireless channel C is changed to the frame offset C from the frame offsets A and B in the sending side, a gap (no signal interval) is generated between the wireless channels A, B and the wireless channel C as shown in FIG. 5. As a result, in the receiving side, there occurs instantaneous interruption in the bearer service data A and B respectively. Thus, it is impossible to perform bearer integration between wireless channels which have different frame offsets without instantaneous interruption.
According to the above-mentioned conventional method, bearer integration is not available for the bearer service which does not permit the instantaneous interruption. In addition, the number of the wireless channels can not be increased due to such a restriction.